Tetrahydroxydiboron

1.  Reagent used for the palladium-catalyzed aryl borylation of aryl halides.
2.  Reagent used for the copper-catalyzed β-boration of α,β-unsaturated carbonyl compounds.
3.  Reagent used for the nickel-catayzed (het)aryl borylation of aryl halides.
4.  Reagent used for the palladium-catalyzed borylation of allylic alcohols.

7732-18-5

158752-98-8

13675-18-8

Tetrakis(pyrrolidino)diborane (0.1 mole) was added to a three-necked flask equipped with a titration and refluxing device under a nitrogen atmosphere with 50-60 times the volume of electrophoretic grade deionized water. The temperature of the reaction system was raised to 100 °C and the reaction was refluxed for 1.5 hours. Subsequently, the unit was replaced with an atmospheric pressure distillation unit and distilled to remove the tetrahydropyrrole generated in the reaction. After the tetrandrine was completely evaporated, the reaction solution was cooled to room temperature, at which point a solid precipitated. The solid was collected by filtration and dried to give 8.5 g of white solid tetrahydroxydiboron, which was analyzed by HNMR to confirm that the purity was greater than 98%, which was consistent with literature reports. The resulting tetrahydroxydiboron was dissolved in 45 mL of methanol and stirred at room temperature until completely dissolved (took about 10-15 min). Subsequently, aqueous KHF2 solution (0.38 mol) was added and stirring was continued for 1 h at room temperature. After completion of the reaction, the system was left to stratify and the lower liquid was carefully separated. The lower liquid was distilled to dryness, acetone was added and the mixture was filtered to give 15.8 g of white solid potassium boron trifluoride in 74% overall yield.